The present invention contains material which is related to application Ser. No. 07/832,118 filed on Feb. 6, 1992, in behalf of Schellinger et al. and assigned to the assignee of the present invention.
A cordless telephone system typically includes a portable cordless handset and a cordless base station connected to a telephone company phone system (TELCO) by telephone landlines. The cordless base station has an assigned landline telephone number that allows the user to place and receive calls using the cordless portable handset within a limited range of the cordless base station, such as in a home. However, due to their limited range, the cordless portable handset provides the user with relatively local radiotelephone communication.
Radiotelephone communication outside the range of the cordless telephone system may also be provided to the user via a cellular telephone system. A cellular telephone system typically includes cellular subscriber units (mobile or portable)and cellular base stations connected to the TELCO via one or more cellular switching networks. Each cellular subscriber unit has an assigned cellular telephone number that allows the user to place and receive calls within a widespread range of the cellular base stations, such as throughout a metropolitan area. However, the cost of using the cellular telephone service is generally greater than the cordless telephone service.
To reduce this problem, a radiotelephone may access both the wide area cellular telephone system and the lower cost cordless base station at the user's home. It is also possible to access a microcellular telephone system in those locations where such a system offers radio coverage.
A radiotelephone which transmits and receives calls in both a cellular and a cordless system should have the capability of selecting a system into which it is to operate. An automatic system selection should be made on parameters advantageous to the user. It is important that the radiotelephone, regardless of which system is selected, not miss calls directed to it.
Accordingly, there is a need for a radiotelephone system that enables a user to receive incoming calls via both a short range system such as a cordless system and a wide area system like a cellular telephone system without excessive loss of incoming calls.